1. Field of the Invention
The present invention relates to a method for detecting the physiological condition of a sleeping patient.
2. Related Art
The sleep condition (depth of a sleep) of a patient is usually detected from a polysomnogram which shows signals which are simultaneously measured on the patient's body by a polysomnographer. The polysomnogram includes an electroencephalogram, an oclogram, an electromyogramn, an electrocardiogram and the like. The patient needs to be hospitalized for such measurement, because the polysomnographer is a large-scaled facility. Further, the patient feels uncomfortable during the measurement, because sensors are attached on his/her head and face. Accordingly, the patient's sleep is disturbed and, as a result, accurate data is not obtained.
JP-A-3-41926 discloses an alternative method for detecting a sleep condition of a patient. The method detects a respiration rate and a pulse rate of the patient, and determines the patient's sleep condition based on the detected respiration rate and pulse rate as follows. The Pulse period, which corresponds to the R-R period in the electrocardiogram, is calculated, and thereafter the sleep condition (REM sleep or non-REM sleep) is detected from the fluctuation of the pulse period. In order to obtain the pulse period, the peak (top or bottom) of every pulse wave should be accurately detected. When pulse waves fluctuate regularly, the peaks of the pulse waves can be detected accurately. However, pulse waves may fluctuate irregularly if the patient moves his/her body during sleep. In this case, the peaks of pulse waves may shift due to a factor other than the fluctuation of blood flow and consequently may be incorrectly detected. In order to obtain the pulse period based on the peaks of the pulse waves which may be provided as the result of the misdetection, complicated calculations are required. Accordingly, this method cannot readily detect the patient's sleep condition.
Further, the pulse period varies distinctly depending on whether the patient is in the REM sleep or non-REM sleep, only when the patient is healthy. When the patient is ill or old, the pulse period varies only slightly depending on whether the patient is in the REM sleep or non-REM sleep. Accordingly it is difficult to detect the sleep condition.
The diagnosis of sleep apnea syndrome is also made by examining all the signals in the polysomnogram. Therefore it is expensive and requires time and effort for a patient to have examination for sleep apnea syndrome, because the patient needs to be hospitalized. As a result, it is difficult to detect and treat the sleep apnea syndrome early.